Drug screening has been conducted by measuring the electrical activity of a cell exposed to a drug. Typically, the electrical activity of a cell is measured by a patch clamp method, a method employing a fluorescent pigment or a light emitting indicator, or the like.
In the patch clamp method, a small portion (patch) of cell membrane, which is attached to a tip portion of a micropipette, is used to electrically record ion transport through a single ion channel protein. The patch clamp method is one of a few number of cell biological techniques which can be used to investigate the function of a single protein molecule in real time (see, e.g., Molecular Biology of the Cell, 3rd Ed., Garland Publishing, Inc., New York, 1994, Japanese Version, translation supervised by Keiko Nakamura et al., pp. 181–182, 1995, Kyoikusha). The electrical activity of a cell is also measured by a combination of a light emitting indicator or a fluorescent pigment, which emits light in response to a change in the concentration of a particular ion, with a state-of-the-art image processing method (e.g., a fluorescent image of a cell is taken by a CCD camera or the like to monitor intracellular ion transport).
The patch clamp method requires special techniques for preparation of a micropipette and the like. Therefore, the patch clamp method is not suitable for screening a large quantity of candidate compounds for a drug at high speed. The method using a fluorescent pigment or the like can screen a large quantity of candidate compounds for a drug at high speed. However, this method requires a step of staining cells. During measurement, pigments cause high background noise, and the fluorescence intensity decreases with time, resulting in poor signal to noise ratio (S/N). There is a demand for a cell potential measuring device with which data having substantially the same quality as that obtained by a patch clamp method can be obtained and which can be performed simply, quickly and automatically, as with the fluorescent pigment method.
An object of the present invention is to improve conventional apparatuses for measuring the electrical activities of cells as described above and to provide a sensor capable of simply and quickly measuring the electrical activities of a number of cells simultaneously and a device capable of detecting signal transmission between subject cells.